I will have a total of 6 new credit cards with credit history year of 2011, but the AmEx was backdated to 1989, but the rest of them will be 2011. Only AmEx and Wells Fargo started reporting, and my EQ Fico score is currently at 780 and EX and TU Fako scores at at 790. I'm assuming they will drop once other cards start reporting and dilute AAoA. On average, how long will new accounts impact the score and how much?

New accounts will always impact your score because they are always the ones hurting your AAoA. I'm not sure what you're trying to ask there. No one can really quantify how much new accounts will hurt your score because, as you'd expect, everyone has a different history and different results.

Judging from your other post, it looks like you have 1 account dating 1989 and 5 accounts dating Aug or Sept 2011. Without actually doing any math, it's obvious that your AAoA is going to take a huge hit because you have five 1-2 month old accounts and one 264 month old account (assuming Sept 1989). The math comes out to a new AAoA of about 45 months rather than 264 months prior to opening your 5 new accounts.

However, your 5 new accounts have helped your utilization ratio, so even though your AAoA will have a negative impact on your score, your util will help (assuming your 5 cards didn't all have small "toy" CLs).

Also, the inquiries will hurt your score for now but I believe they fall off every 12 months.